I am struggling with building a table for my Lowrider 3. I am doing a slightly oversize 4x8’ working area at 50" x 98" to be able to handle full sheets of MDF which are 49" x 97". I had thought about doing a torsion box to keep it nice and flat but there’s really no way to go any bigger than a standard sheet of MDF unless you start putting together multiple sheets. Perhaps that is the only way? My only other thought was to make the 49" x 97" torsion box in the middle like Doug’s from Design 8 studio and with the runners on the side and just have an extra 1" on each side that is technically usable, but will not have support under it.
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I don’t see any reason you need full sheets for the faces, you just need a way to make sure that any forces are being transferred around the structure appropriately.
One option would be to make a 50" x 98" sheet by laminating up smaller, thinner sheets. Say 3x 50"x 33" and then 2x 50"x33" and 2x50" x 15". That would give a significant amount of overlap in the seams. I think that’d probably be overkill, though. (Edit: Obviously the table would need to be larger than 50x98, I’m just not used to thinking in inches. The idea is still the same: Use multiple smaller pieces tiled out, rather than one big piece)
The other option would be to just make the faces as whatever size is convenient and then make sure the ribs are constructed such that you can fix the faces to the ribs well at the joint. Or come back afterwards and add cleats across the underside of the joint anywhere that isn’t supported. That kind of thing.
Or just make it up as multiple smaller torsion boxes and then bolt them together. That’s probably a better way to do it, anyway, especially if you’re going to add a frame under it or feet that allow it to be leveled separately anyway.
Edit: Also, perhaps check with your local suppliers. I just checked and it looks like you’d need a table that’s 62.5"x113". I can order MDF in oversized sheets in a range of sizes up to 144" x 72". That could be used if you wanted to just do it as a single big table with single sheets etc.
My table is 63" x 120". Although mine is not a full torsion box, I did more or less as @Jono is suggesting, and used a full sheet of ply along with a couple of smaller cuts, and used the ribs as the joint where possible.
Baltic birch plywood is commonly available in 5’x5’ sheets and 5’x10’ sheets are also available but they’re not a common big box store item, you’d have to shop around to find a specialty supplier that carries them.
My table overall is 6x10 and I ended up using three pieces at 40” x 72”. Still debating on adding some tenons to help keep things nice and flat, but a permanent torsion box underneath would probably solve that issue too.
Thanks for all the comments. Lots of good ideas here. I had forgotten about 5x5 sheets. I do know a local plywood supplier that sells 5x5 Baltic birch but I do worry about the cost. Perhaps 1/2" sheets won’t be as bad but I think last time I got 5x5 sheets they were over $100 a piece. I checked with another supplier that is a bit far from me and theirs is $88 a sheet. Yikes. Needing at least 4 adds up fast. I suppose I could still use MDF for the inners but that’s really starting to add up.
I suppose I can check and see if the plywood supplier also has any specialty sized MDF panels. Otherwise its sound like a triple torsion box table (3 x 40"x70") with some way to bolt them together might not be a bad idea but a lot of work. Perhaps something like a 3 piece Ron Paulk Workbench. https://www.youtube.com/watch?v=KnNi6Tpp-ac Do the side cutouts and use screw knobs with T nuts to pull it together on the sides. Might have to model this up.
Mine was a two part paulk inspired table. I used 10’ peices of unistrut for the rollers to ride on. The table surface itself was only 8’ long by 6’ wide.